1. Field of the Invention
The present invention relates to an inkjet print head wherein the surface (front surface) for ejecting an ink droplet from an ink channel partitioned by a drive wall composed of piezoelectric devices and the surface (back surface) for supplying ink to the aforementioned ink channel are located face to face with each other.
2. Description of the Related Art
One of the prior art inkjet print heads is a shared wall share mode inkjet print head wherein voltage is applied to the drive wall partitioning an ink channel so that the drive wall is shear-deformed, and the pressure resulting therefrom is utilized to allow ink of the ink channel to be ejected through a nozzle. The Official Gazette of Japanese Patent Tokkai 2002-264342 discloses a share mode inkjet print head, as one of these inkjet print heads, wherein the surface (front surface) for ejecting ink from an ink channel and the surface (back surface) for supplying ink to the aforementioned ink channel are located face to face with each other.
In the aforementioned inkjet print head, the wire for electrical connection between a drive electrode and a drive circuit is led from inside the ink channel up to the outer surface of the head chip so that the FPC (flexible printed circuit board) and others can be connected.
Thus, according to the Official Gazette of Japanese Patent Tokkai 2002-264342, a plurality of straight ink channels with respect to a piezoelectric device substrate are formed by grooving in parallel. Then a plating catalyst is adsorbed, and a thin metal layer is formed on the whole surface by electroless plating. The plated metal film on unwanted positions among ink channels is removed by applying a laser beam all over the head chip to make a wiring pattern, and then plating is provided again to grow the pattern to the desired thickness. Thus, the wire for allowing each drive electrode to conduct is routed all over the head chip. In this case, however, the wire for conducting with the drive electrode is formed so that it will be routed in 3D configuration from inside the ink channel to the back surface of the head chip through the front and back surfaces of the head chip. As a result, the wire is bought into contact with a plurality of the corners of the head chips. The portions in contact therewith tend to cause wire disconnection. This raises a problem with unreliable conduction.
In the Official Gazette of Japanese Patent Tokkai 2001-63043, a wiring pattern of the drive wire for electrical connection of the drive circuit to the nozzle plate with a nozzle formed thereon is formed integrally, and this nozzle plate is attached to the ink outlet side. After that, the side with the aforementioned wiring pattern formed thereon is bent, and electrical connection is made between the connection wire led out onto the top surface of the head chip and the aforementioned drive wire. This technique is disclosed in the aforementioned Official Gazette of Japanese Patent Tokkai 2001-63043.
As described in the Official Gazette of Japanese Patent Tokkai 2001-63043, however, when the drive wire is formed integrally with the nozzle plate, bonding work is so complicated that a bonding failure easily occurs. This is because the nozzle is generally required to be processed to a high precision; hence, it is formed in advance before being bonded with a head chip. To put it another way, in the step of bonding the nozzle, alignment work is essential to ensure exact correspondence between each nozzle and ink channel. Accordingly, when the drive wire is formed integrally with the nozzle plate, both connection between wires and precise alignment between the nozzle and ink channel must be carried out simultaneously.
Further, when a multi-nozzle structure is to be adopted for the purpose of creating a more densely packed inkjet print head, one of the possible methods is to stack a plurality of head chips in multiple layers in the direction orthogonal to the channel arrangement, whereby ink channels in a plurality of rows are created. As described above with reference to the prior art, however, a flexible wiring board is connected to the top surface or bottom surface of the head chip configured in such a way that the front surface and back surface of the head chip are located face to face with each other. When a multi-nozzle row structure is to be adopted using such a head chip, the surface connected with the flexible wiring board is commonly bonded with the opposite surface thereof. According to this method, head chips are stacked in two layers in vertical direction, and ink channels can be formed in two rows alone. Accordingly, the only way of increasing the number of nozzles is to increase the number of the ink channels of each head chip in the direction wherein the ink channels are arranged.